<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <link rel="stylesheet" href="DropDownLss.css"/>
</head>
<body>
    <ul class="dropDown">
        <li>下拉菜单<span class="triangle"></span></li>
        <li>选项一</li>
        <li>选项二</li>
        <li>选项三</li>
        <li>选项四</li>
    </ul>
</body>
</html>